Crew members of an ill-fated Amtrak train applied the brakes after noticing a problem on the tracks ahead but didn’t have enough time to avoid a collision with another train, federal investigators say.

That crash killed two Amtrak crew members and injured more than 100 passengers near Cayce early Sunday.

During a news conference Monday not far from the S.C. crash site, National Transportation Safety Board chairman Robert Sumwalt said the Amtrak train smashed head-on with the locomotive of the parked CSX train after the passenger train ran off the main line.

The Amtrak train’s brakes were applied only five seconds before a recording of the crash ended, indicating the crew had almost no time to react before the impact, according to information investigators have obtained. The train was moving at 50 mph at the time of impact, down from the 56 mph speed it had been traveling, Sumwalt said.

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The collision, which pushed the CSX train 15 feet from its parked position, occurred because a switch was not set in the right position, his agency says. That forced the passenger train off the main track.

Information supplied at Monday’s news conference came from event recorders that had been recovered from the train wreckage by the NTSB, which investigates all major railroad accidents.

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See the Amtrak train crash from the air by Charleston Highway captured by drone. The train crash occurred on Feb. 4, 2018 that resulted in two deaths and critical injuries for over 100 passengers on board. Jeff Blake

The Cayce crash has revived debate as to why the United States still has not installed positive train control on much of the nation’s railroad tracks.

Sumwalt said the Cayce accident and others around the country could have been avoided if such controls were in place, but that Congress had delayed them.

The biggest question is why the switch was set to divert traffic off the main line — and who is responsible.

Sumwalt said investigators interviewed four CSX workers Monday and would be conducting more interviews this week as they seek more answers. He declined to say what investigators had learned from the interviews so far. Those interviewed were the CSX train conductor, its engineer, a dispatcher and a train master, he said.

On Tuesday, the NTSB will interview Amtrak crew members, he said.

“A lot has been done today and a lot needs to be done,” Sumwalt said. “I’m confident that our investigators will be able to piece the facts together.”

The NTSB has said CSX is responsible for maintaining the track switch in the proper position. Sumwalt on Sunday said the wreck was a result of a “tragic human error.” But, on Monday, he declined to point the finger at a CSX employee.

“We’re not saying (that one of the CSX employees made a mistake),” Sumwalt said. “We’re investigating why it’s the case that this switch was like this.”

The Cayce train wreck, in some ways, is similar to a disastrous Norfolk Southern train crash in Graniteville 13 years ago. That wreck left nine dead after a train crew failed to return a track switch in the proper position.

In Graniteville, a freight train ran off the main line and smashed into parked rail cars. Nine area residents died in a cloud of toxic chlorine that was released in the collision. Norfolk Southern, ultimately, fired the train’s crew.

CSX operates about 1,800 miles of track in South Carolina, maintaining 1,750 public and private grade crossings, according to the company’s website. The company said it is cooperating with the investigation.

Sumwalt said equipment from the wrecked trains has been moved to an area near the crash site and is being examined.